Erythropoietic protoporphyria (EPP) is caused by ferrochelatase deficiency. The accumulated photosensitising compound and the characteristic feature distinguishing it from other porphyrias is:

• A Uroporphyrin accumulation; vesicles/bullae on sun-exposed areas
• B Coproporphyrin III accumulation; neuropsychiatric symptoms
• C Protoporphyrin IX accumulation; painful burning sensation (non-blistering) immediately upon light exposure ✓
• D ALA and PBG accumulation; acute abdominal attacks

Explanation

Ferrochelatase inserts Fe2+ into protoporphyrin IX to form heme (final step of heme synthesis). Its deficiency causes protoporphyrin IX (PPIX) accumulation in erythrocytes, plasma, and skin. PPIX is a potent photosensitiser: it absorbs the Soret band (~400 nm visible light), generating singlet oxygen and reactive species that cause an immediate burning/itching sensation upon sunlight exposure. Crucially, EPP does NOT cause blistering (unlike PCT/CEP/HEP which produce uroporphyrin/photooxidation-induced blistering). Liver damage from PPIX accumulation (biliary stones, cirrhosis) is the major long-term complication.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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Written and medically reviewed by the StethoPrep medical team.